Christensen T, Riis AH, Hatch EE, Wise LA, Nielsen MG, Rothman KJ, Toft Sorensen H, Mikkelsen EM. Costs and efficiency of online and offline recruitment methods: a web-based cohort study. J Med Internet Res. 2017 Mar 1;19(3):e58. doi: 10.2196/jmir.6716
Mansfield CA, Van Houtven G, Huber J. The efficiency of political mechanisms for siting nuisance facilities: are opponents more likely to participate than supporters? J Real Estate Financ Econ. 2001;22(2/3):141-62.